From what I have seen it just appears to be a personal thing. both pretty much do what the other does.
I really liked the screen on the apex but it was more money so I went with the RKE. I'm more budget minded I guess plus i don't see the need to be able to control my tank via the internet. LOL
Not sure how you program the apex either, I know the RKE plugs into my computer and you program it like that, very very easy. It's also pretty easy to navigate the home screen without the computer to program it.
The ONLY thing so far that has me confused with the RKE is the ATO float switch. It looks like I might have to connect wires rather than just plug into the port. That I;m not too happy about. But I havent really messed with it yet so I dont know how hard or easy it will be.